There is a switching regulator as a circuit converting an input direct-current voltage to output a direct-current voltage having different electric potential. The switching regulator includes a synchronously rectifying switching regulator, which is provided with a driving switching element and a rectifying switching element. The driving switching element applies a direct-current power source voltage supplied from a direct-current power source, such as a battery, to an inductor (coil) to flow an electric current and accumulate energy in the coil. The rectifying switching element rectifies a coil current in an energy discharging period, in which the driving switching element is off. The synchronously rectifying switching regulator turning on and off the driving switching element and the rectifying switching element complementarily to enhance the power efficiency thereof in comparison with a diode rectifying switching regulator.
The synchronously rectifying switching regulator has the problem of the lowering of the power efficiency at the time of a light load, and accordingly various inventions have hitherto been proposed in order to settle this problem (see, for example, Japanese Patent Application Laid-Open Publication No. 2000-092824). Furthermore, a similar problem exists in an insulated switching regulator, using a transformer, and accordingly various inventions for settling this problem have also proposed (see, for example, Japanese Patent Application Laid-Open Publication No. Hei 05-022936).